An image processing apparatus such as an image forming apparatus forms a toner image on an image carrier, and transfers the toner image from the image carrier onto a recording sheet. The toner that resides on the image carrier after transfer of the toner image is removed by a cleaning device and stored in a collected toner container. The collected toner container needs to be replaced with an empty collected toner container before it becomes full of the collected toner. If the collected toner container full of the collected toner is not replaced, the collected toner may overflow and contaminate a recording sheet or nearby devices within the image processing apparatus, which may further damage the device.
In order to assist an operator to replace the collected toner container before it becomes full, the amount of collected toner that is accumulated in the collected toner container needs to be obtained. For example, the collected toner container may be provided with a detector, such as an optical sensor, that detects an amount of collected toner as described in Japanese Patent Application Publication Nos. H11-133810-A and H11-174917-A. However, a detection result output by the detector may not be accurate if toner is adhered to a surface of the detector. Further, manufacturing or maintenance cost of the image processing apparatus may increase if the detector is to be provided.
Japanese Patent Application Publication No. 2005-241676 discloses a technique that calculates an amount of collected toner accumulated in the collected toner container based on information regarding toner consumption. Alternatively, the image processing apparatus may be designed to request the operator to replace the collected toner container when a toner cartridge becomes empty, based on the assumption that the collected toner container and the toner cartridge have substantially the same life cycle. These cases, however, fail to address the problem that the amount of collected toner per printing operation varies depending on the conditions under which the printing operation is performed.
For example, when the image processing apparatus prints an image with a low printing ratio according to a user instruction, the amount of toner to be transferred onto the recording sheet decreases such that the amount of collected toner increases.
In another example, when a number of pages to be printed per printing operation is small, time in which a photoconductor or a developer is rotated without feeding a recording sheet increases with respect to the overall time required for completing printing operation. This is because the photoconductor or the developer is rotated for a predetermined time period before starting actual printing operation, either at the start of the printing operation or at the end the printing operation, in order to maintain a constant level of toner density or throughput. Accordingly, the amount of toner to be transferred onto the recoding sheet decreases such that the amount of collected toner increases.
When the image processing apparatus performs successive printing operations under either or both of the above scenarios, toner may overflow from the full collected toner container before the toner cartridge is emptied.